Low angle light scattering studies on whole, half, and quarter molecules of T2 bacteriophage DNA

Static light scattering measurements have been made at angles as low as 8 degrees on whole, half, and quarter molecules of native, T2 bacteriophage DNA in 0.195 M Na+. The fragments were obtained by high-speed stirring of the native DNA, and fractionated on methylated-albumin-kieselguhr columns. Accompanying measurements of sedimentation coefficients and intrinsic viscosities were made. Because linear extrapolations of light scattering data above 8 degrees for these samples were suspect, the measurements were analyzed by fitting curves calculated from the theory of wormlike coils to experimental curves at c = 0. Results showed that the excluded volume parameter, epsilon, must be used in analyzing the scattering curves; a reasonable value of epsilon was 0.08, in agreement with that found for T7 DNA (Harpst, J. A. 1980. Biophys. Chem. 11:295-302). The persistence length of all three DNAs in this paper was 50 +/- 5 nm, showed no dependence on molecular weight, but was somewhat below that reported previously for T7 DNA (60 nm). Theoretical curves calculated with the preceding parameters had a clear upward curvature in scattering envelopes below 8 degrees for quarter and half molecules, but such curvature was minimal for whole T2 DNA, so that linear extrapolations of experimental data above 8 degrees gave a molecular weight and root-mean-square radius which were nearly the same as those from theory. The molecular weight and radius for whole T2, derived from the comparison of theory and experiment, were 115 X 10(6) and 1,224 nm, respectively. The measurements on T2 DNA were clearly at the upper limit of current techniques.